These fees are in addition to the customs duties and taxes imposed by country tax and customs officials.

And

The first payment goes to the seller and consists of the item cost and the domestic postage costs. The second payment goes to the global postage provider and consists of the international postage costs and any import charges.

Between those two, I think the fees are summed up. The seller ships (domestic) to a third party. The third party handles international shipment, and collects their own fees, which appear to be based on the value of the item being shipped (so "insurance" based on value is included).

I would never use a service such as this, personally. If I really needed to, I would ask eBay, PayPal, the shipping service and the seller - "Who is responsible for the item, and when? If I need to file a claim, where do I do so, and who is responsible for investigating/paying out? If an item gets lost or damaged, where did it happen in this process? How can that be confirmed or investigated? Is domestic shipping tracked? International? Separately or together?" I could think of ten more questions, and I don't think most of them could be answered to my satisfaction.